Polythiophene (PT) is an important conjugated polymer that finds applications in electronic and molecular electronic devices. Considering its application area, its electrical conductivity is of major concern. In the present work electrical conductivity (σ) measurements of chemically synthesized and FeCl3 doped PT samples were carried out using a two probe method by applying voltages from 0 V to 100 V in the temperature range from 313 K to 373 K. There was an increase in electrical conductivity by two orders of magnitude after doping. I–V characteristic curves of undoped and doped samples show negative resistance behavior. From log σ versus 1/T graphs it was found that all doped samples showed a metallic nature, where as undoped polythiophene showed a semiconducting nature. Magnetic susceptibility measurements of all samples were carried out using Guoy's method in the temperature range from 300 K to 500 K to characterize the predominant charge carriers. They revealed that the undoped sample was completely diamagnetic in nature where as for the doped samples a number of transitions from diamagnetic to paramagnetic and vice versa were observed with increase in temperature.